ct圖像質量講義(文件)
【正文】 reas where image not faithful to subject ?Sources ? patient ? image process ? equipment Gee David Motion Artifacts ?Causes streaks in image ?Algorithms have trouble coping because of inconsistent data Gee David Artifacts: Abrupt High Contrast Changes ? Examples: ?prostheses ?dental fillings ?surgical clips ?Electrodes ?bone ? Metal absorbs all radiation in ray ?causes starshaped artifact ? Artifact can be reduced by software Gee David ?Increase in mean energy of polychromatic beam as it passes through patient ?Can cause broad dark bands or streaks ? cupping artifact ?Minimized using beam hardening correction algorithms CT Artifacts: Beam Hardening MARS：減除金屬和硬化偽影 Gee David CT Artifacts: Partial Volume Effect ? CT ’s based on linear attenuation coefficient for tissue voxels ? If voxel nonuniform (contains several materials), detection process will average ? Can appear as ? incorrect densities ? Streaks and bands ? Minimizing ? Use thinner slices Gee David Gee David 謝 謝！ Gee David ?描述 CT 圖像質量的三個主要參數(shù) : 空間分辨率、密度分辨率、噪聲 ?對比度 (密度 )分辨率 : 指當細節(jié)與背景之間具有低對比度時，將一定大小的細節(jié)從背景中辨別出來的能力。式中 T表示標稱層厚， D（ z）表示沿垂直于斷層平面的 z軸方向的劑量分布曲線， 是用筆形電離室測量的，積分區(qū)間恒定為 100 mm，表示 單層掃描的劑量 。 DLP=CTDIvol Scan length （ mGy） ED（ effective do
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